Electrophotographic photosensitive plate

ABSTRACT

Electrophotographic photosensitive plate of improved moisture fastness having on its photoconductive layer a protective coating comprising polyvinyl butyral and a cellulose derivative which provides the plate with protection from abrasion and deterioration in resolving power under either high or low humidity conditions.

United States Patent 91 Hukase et al.

[ 51 Nov. 26, 1974 ELECTROPHOTOGRAPHIC PHOTOSENSITIVE PLATE Inventors:Masahiro Hukase; Makoto Tomono;

Sigero Inowa, all of Tokyo, Japan Foreign Application Priority Data July26, 1971 Japan 46-55877 US. Cl 96/l.8, 96/l.5, 117/218 Int. Cl. 603g5/00, G03g 5/02 Field of Search 96/1.5, 1.8; 117/215, 218

References Cited UNITED STATES PATENTS 8/1957 Ullrich 96/l.5 X 11/1958Daubner 117/17.5 X

3,127,331 3/1964 Neber 96/1.5 X

3,140,174 7/1964 Clark 96/1.8 X

3,170,790 2/1965 Clark 96/l.5 X

3,355,289 11/1967 Hall et al. 96/1.5 X

3,434,832 3/1969 Joseph et al. 96/1.5

3,652,268 3/1972 Rowe i i. 96/1.5 3,761,259 9/1973 Arai et a1 117/218 XPrimary Examiner-David Klein Assistant ExaminerJohn R. Miller Attorney,Agent, or FirmWaters, Roditi, Schwartz, & Nissen [57] ABSTRACTElectrophotographic photosensitive plate of improved moisture fastnesshaving on its photoconductive layer a protective coating comprisingpolyvinyl butyral and a cellulose derivative which provides the platewith protection from abrasion and deterioration in resolving power undereither high or low humidity conditrons.

6 Claims, N0 Drawings Dessauer et al. 96/1.5 X

ELECTROPHOTOGRAPHIC PHOTQSENSITIVE PLATE This invention relates to anelectrophotographic pho- In general, the conventionalelectrophotographic process is carried out in such a manner that aphotosensitive plate, prepared by forming a photoconductive layer on anelectroconductive support, is positively or negatively charged(according to the characteristics of the photosensitive plate) by meansof corona discharge, and then exposed to electromagnetic waves, e.g.light or X-ray, to form a latent electrostatic image by utilization ofthe photoconductivity of the photosensitive plate. This latent image isdeveloped with a toner which has been charged with a polarity oppositeto that of said latent image, and, if the developed image is carried onthe photosensitive layer (this means that the photosensitive layerserves as a recording layer as in the Electrofax process), this is fixedas is by application of heat or solvent vapors, while if the recordinglayer is used separately from the photosensitive layer (as in the Xeroxsystem using a selenium photosensitive plate or the like), the developedtoner image is transferred, according to the electrostatic imagetransfer process, to a recording layer, ordinarily on a separate paper,and is then fixed. After the fixing, the photosensitive plate issubjected to cleaning and is reused. Thus, a single photosensitive plateis subjected to a copying cycle comprising charging, imagewise exposure,toner development and fixing optionally with image transfer, repeatedly,as often several thousand times.

The present invention is concerned with an improvement of thephotosensitive plate to be used in the latter process.

Photosensitive plates used in the latter process are abraded or injuredduring cleaning. transfer, and the like mechanical operations. Suchtroubles become fatal drawbacks for the photosensitive plates.Particularly in xeroradiography, relatively many operations are effectedmanually, so that such troubles as mentioned above tend to take place.

Among photosensitive layers, the photoconductive However, the protectivecoating should, of course,

not deprive the photosensitive plate of its inherent characteristics,and should satisfy such conditions as mentioned below.

I. The coating should not react with the photoconductive substance used.

2. The coating should adhere well to the photoconductive layer.

3. In case the photoconductive layer is composed of selenium or itsalloy, the heat treatment for forming the protective coating should notbe effected over a long period of time when the heating temperatureisabove 40C.

4. The coating should not'have an electric conductivity in thehorizontal direction so as not to degrade the photosensitive plate incontrast or resolving power.

5. The coating should not have a volume electric resistivity of morethan 10 cm, because in winter, when the air is dry, the photosensitiveplate is deteriorated in resolving power due to high electricresistance.

6. The coating should be excellent in abrasion resistance.

7. The coating should have such a thickness as not to deteriorate thephotosensitive plate in resolving power and abrasion resistance.

8. The coating should be excellent in moisture fastness.

However, the protective coatings disclosed in the aforesaid prior artliterature are composed of polystyrene, polycarbonate, polyvinyl formal,polyvinyl acetal, cellulose acetate, etc. which heretofore have not beensatisfactory. Although these known protective coatings are relativelysatisfactory in abrasion resistance, they are low in moisture fastnessand hence cannot be used throughout the year, including summer, when thetemperature and humidity are high and winter when the temperature andhumidity are low.

The present invention provides a novel protective coating which hasovercome the drawbacks of the conventionally known protective coatings.That is, the present invention is concerned with an electrophotographicphotosensitive plate prepared by using, as a support, a metal such asaluminum, zinc, brass or copper, or an electroconductive glass, forming,on said electroconductive support, a photoconductive layer composed ofselenium, selenium-tellurium or the like selenium alloy, zinc oxide,lead oxide or cadmium sulfide. and further forming on saidphotoconductive layer a protective layer comprising a mixture ofpolyvinyl butyral and a cellulose derivative which is compatible withthe polyvinyl butyral and which itself has a low volume resistivity.

Polyvinyl butyral having a butyralation degree'within the range of 57 to65 mole percent gives particularly favorable results. Representativeexamples of suitable cellulose derivatives include ethyl cellulose,cellulose diacetate, cellulose triacetate, cellulose propionate,cellulose acetobutyrate and cellulose nitrate. Satisfactory results areobtainable when the proportion of the above-mentioned cellulosederivative based on the amount of polyvinyl butyral is, for example, 20to 50 percent by weight in the case of cellulose nitrate, 10 to 30percent by weight in the case of cellulose diacetate, 20 to 28 percentby weight in the case of cellulose triacetate, and 10 to 30 percent byweight in the case of cellulose acetobutyrate. Thus, the proportion ofthe cellulose derivative used is not fixed but varies depending on thenature of the cellulose derivative employed.

In forming the protective layer according to the present invention, amixture of the above-mentioned two components is dissolved in dioxane orthe like organic solvent therefor and then coated on the photoconductivelayer of the photosensitive plate. When it is desired to form theprotective layer by a dipping method, the said mixture may be dissolvedin a proportion of 3 to 4 g. per I00 cc. of the solvent.

If the protective coating is made thicker, the photosensitive plate isdeteriorated in resolving power and When a protective layer-formingsolution identical in composition with that used in the dipping methodis coated by means ofa whirler, innumerable radial wrinkles are formedon the resulting protective layer. If, in;

this case, more than 3 percent by weight of ethyl cellulose isincorporated into said solution, the resulting protective layer will befree of radial wrinkles and will provide a uniform surface. However,when the content of ethyl cellulose is excessively high, undesirableresults are brought about under conditions of low humidity. Ordinarily,therefore, an ethyl cellulose content of about 3 to 8 percent by weightis preferred.

The photosensitive plate of the present invention not only has a highresolving power under high humidity conditions but also is greatlyimproved in image characteristics even under low humidity conditions,and thus is high in resolving power and excellent in resistance toabrasion and injury. For example, the photosensitive plate of thepresent invention is 3 to 4 times higher in abrasion resistance than aphotosensitive plate having a protective coating composed of only thecellulose derivative. Furthermore, a photosensitive plate having aprotective coating composed of only the cellulose derivative isdeteriorated in resolving power under high humidity conditions, whereasthe photosensitive plate of the present invention shows a high resolvingpower at a humidity within the range of from 30 to 90 percent. Forobtaining a good image, a resolving power of at least tl to lq lings permm. is necessary.

Photosensitive selenium plates-having protective layers, whereinpolyvinyl butyral andtypical cellulose derivatives were singly used,were tested in resolving power under various humidity conditions. Theresults obtained were as set forth in Table l, in which the values ofresolving power are represented by lines per mm.

Table 1 useful. This, however, is not practical because adsorption ofwater and absorption of moisture would be increased under high humidityconditions.

As will be understood from Table l, the present invention provides aprotective layer which can be rendered free of the drawbacks ofconventionally known protective layers. It is very surprising that thedrawbacks encountered when a polyvinyl butyral or a cellulose derivativeis used alone by itself can be removed by the joint use of these two.

The present invention is illustrated in further detail below withreference to the following representative, non-limiting examples.

Example 1 3 grams ofa mixture constituting a protective coatingcomposition comprising percent by weight of polyvinyl butyral (EslecBM-2 produced by Sekisui Chemical Co.) and 30 percent byweight ofcellulose nitrate (FQ produced by Daicel Co.) was dissolved in 100 cc.of dioxane. The resulting solution was'coated in accor dance with aconventional dipping method on a photosensitive selenium plate to athickness of about l u, whereby the photosensitive plate showed anexcellent abrasion resistance and a high resolving power of 8 to 10lines per mm. at a humidity within the range from 30 to 90 percent.

Example 2 3 grams of a mixture comprising percent by weight of polyvinylbutyral (Eslec BM-2 produced by Sekisui Chemical Co.) and 25 percent byweight of cellulose diacetate (L-AC produced by Daicel Co.) wasdissolved in 100 cc. of dioxane. The resulting solution was coated inaccordance with a conventional dipping 'method on a photosensitiveselenium plate to a thickness of about 1 .1., whereby the photosensitiveplate showed the same characteristics as in Example 1.

Example 3 4 grams of a mixture comprising 75 percent by weight ofpolyvinyl butyral (Eslec BM-2 produced by Type of protective coatingResolving Power at the given humidity on selenium 38% 57% 68% 8l%Not-protected 12.5 12.5 l0- l0- l0 12.5 12.5 (Butyralation (Residualacetyl degree, mole%) content, mole%) Polyvinyl butyral 57 :l: 3 Lessthan 3 5.0 8-10 8-l0 8-l0 8.0 do. 62 t 3 do. 4.0- 8-10 8-l0 S-lO 8.0

5.0 More than do. 67 4-6 4.0 8.0 6.3 6.3 5.0 Cellulose 6.0 4.0 2.0 0 0dlaeetate Cellulose l0.0 8-10 2.0 0

nitrate 60 Sektsui Chemical Co.) and 25 percent by weight of cel- As isclear from Table l, polyvinyl butyrals having a butyralation degreewithin the range of from 57 to 65 mole percent give favorable results,and those having a butyralation degree of more than 67 mole percent givesomewhat inferior results.

For preventing the degradation in resolving power under low humidityconditions, it might be thought that the addition of an ionic surfaceactive agent would be pt, whereby the photosensitive plate showed thesame characteristics as in Example 1.

Example 4 3 grams of a resin mixture comprising 80 percent by weight ofpolyvinyl butyral (Eslec BM-2 produced by Sekisui Chemical Co.) andpercent by weight of cellulose acetobutyrate (Kodapak lI produced byEastman Kodak Co.) was dissolved in 100 cc. of dioxane. The resultingsolution was coated in accordance with a conventional dipping method ona photosensitive selenium plate to a thickness of about l ,u, wherebythe photosensitive plate showed the same characteristics as in Example1.

Example 5 characteristics as in Example I.

Example 6 3 grams of a resin mixture comprising 65 percent by weight ofpolyvinyl butyral (Eslec BM-Z produced by Sckisui Chemical Co.) and 35percent by weight of cellulose nitrate (FO produced by Daicel Co.) wasdissolved in 100 cc. of dioxane. The resulting solution was coated ontoa 40 .1. thick photosensitive CdS plate to a thickness of about 0.5 ;1.,whereby the photosensitive plate showed the same characteristics as inExample I.

What we claim is:

1. An electrophotographic photosensitive plate, comprising anelectroconductive layer, a photoconductive layer thereon, and aprotective polymer coating layer on the opposite surface of saidphotoconductive layer, said protective coating having a thickness notgreater than one micron and comprising polyvinyl butyral having abutyralation degree of 57 to 65 mole percent and a cellulose derivativeselected from the group consisting of cellulose diacetate. cellulosetriacetate. cellulose propionate, cellulose acetobutyrate, and cellulosenitrate, said polyvinyl butyral being present in said coating in anamount varying from 50 to 90 percent by weight, and said cellulosederivative being present in said coating in an amount ranging from 10 to50 percent, by weight, said protective polymer coating layer having avolume resistivity no greater than 10 ohm- 2. An electrophotographicphotosensitive plate as claimed in claim 1, wherein the protectivepolymer coating layer is composed of 50 to 80 percent by weight ofpolyvinyl butyral and 20 to 50 percent by weight of cellulose nitrate.

3. An electrophotographic photosensitive plate as claimed in claim 1,wherein the protective polymer coating layer is composed of to 90percent by weight of polyvinyl butyral and 10 to 30 percent by weight ofcellulose diacetate.

4. An electrophotographic photosensitive plate as claimed in claim 1,wherein the protective polymer coating layer is composed of 72 topercent by weight of polvinyl butyral and 20 to 28 percent by weight ofcellulose triacetate.

5. An electrophotographic photosensitive plate which comprises, on asupport of an inorganic material selected from the group consisting ofaluminum, zinc, brass, copper, and electroconductive glass, :1photoconductive layer made of a substance selected from the groupconsisting of selenium, selenium-tellurium, zinc oxide, lead oxide andcadmium sulfide and a protective polymer coating layer coated on theopposite surface of said photoconductive layer, said protective coatinghaving a thickness not greater than one micron and comprising apolyvinyl butyral having a butyralation degree of 57 to 65 mole percentand a cellulose derivative compatible with said polyvinyl butyral, saidpolyvinyl butyral being present in said coating in an amount varyingfrom 50 to percent, by weight, and said cellulose derivative beingpresent in said coating in an amount ranging from l0 to 50 percent, byweight, said protective'polymer coating layer having a volumeresistivity no greater than 10 ohm cm.

6. An electrophtograp'hic photosensitive plate, as claimed in claimlwherein said protective polymer coating layer also contains 3 to 8percent of ethyl cellulose.

1. An electrophotographic photosensitive plate, comprising anelectroconductive layer, a photoconductive layer thereon, and aprotective polymer coating layer on the opposite surface of saidphotoconductive layer, said protective coating having a thickness notgreater than one micron and comprising polyvinyl butyral having abutyralation degree of 57 to 65 mole percent and a cellulose derivativeselected from the group consisting of cellulose diacetate, cellulosetriacetate, cellulose propionate, cellulose acetobutyrate, and cellulosenitrate, said polyvinyl butyral being present in said coating in anamount varying from 50 to 90 percent by weight, and said cellulosederivative being present in said coating in an amount ranging from 10 to50 percent, by weight, said protective polymer coating layer having avolume resistivity no greater than 1015 ohm-cm.
 2. Anelectrophotographic photosensitive plate as claimed in claim 1, whereinthe protective polymer coating layer is composed of 50 to 80 percent byweight of polyvinyl butyral and 20 to 50 percent by weight of cellulosenitrate.
 3. An electrophotographic photosensitive plate as claimed inclaim 1, wherein the protective polymer coating layer is composed of 70to 90 percent by weight of polyvinyl butyral and 10 to 30 percent byweight of cellulose diacetate.
 4. An electrophotographic photosensitiveplate as claimed in claim 1, wherein the protective polymer coatinglayer is composed of 72 to 80 percent by weight of polvinyl butyral and20 to 28 percent by weight of cellulose triacetate.
 5. ANELECTROPHOTOGRAPHIC PHOTOSENSITIVE PLATE WHICH COMPRISES, ON A SUPPORTOF AN INORGANIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM,ZINC, BRASS, COPPER, AND ELECTROCONDUCTIVE GLASS, A PHOTOCONDUCTIVE,LAYER MADE OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OFSELENIUM, SELENIUM-TELLURIUM, ZINC OXIDE, LEAD OXIDE AND CADMIUM SULFIDEAND A PROTECTIVE POLYMER COATING LAYER COATED ON THE OPPOSITE SURFACE OFSAID PHOTOCONDUCTIVE LAYER, SAID PROTECTIVE COATING HAVING A THICKNESSNOT GREATER THAN ONE MICRON AND COMPRISING A POLYVINYL BUTYRAL HAVING ABUTYRALATION DEGREE OF 57 TO 65 MOLE PERCENT AND A CELLULOSE DERIVATIVECOMPBATIBLE WITH SAID POLYVINYL BUTRYAL, SAID POLYVINYL BUTYRAL BEINGPRESENT IN SAID COATING IN AN AMOUNT VARYING FROM 50 TO 90 PERCENT, BYWEIGHT, AND SAID CELLULOSE DERIVATIVE BEING PRESENT IN SAID COATING INAN AMOUNT RANGING FROM 10 TO 50 PERCENT, BY WEIGHT, SAID PROTECTIVEPOLYMER COATING LAYER HAVING A VOLUME RESISTIVITY NO GREATER THAN 10**15OHM - CM.
 6. An electrophtographic photosensitive plate, as claimed inclaim 1 wherein said protective polymer coating layer also contains 3 to8 percent of ethyl cellulose.